Transparent glazing and use thereof in a chilling chamber door comprising in particular a glazing under vacuum

ABSTRACT

A transparent glazing unit having at least one viewing area, combined with an antifrosting adsorbent layer deposited on at least one surface of the said area, and its use in a door of a refrigerated enclosure and more particularly a glazed door, the glazed area of which essentially consists of a vacuum glazing unit.

The invention relates to a transparent glazing unit and its use in adoor of a refrigerated enclosure and more particularly to a glazed door,the glazed area of which essentially consists of a vacuum glazing unit.

The invention will be more particularly described with reference todoors of refrigerated enclosures in which cold or frozen products aredisplayed, but the invention must not be construed as being limited toproducts or applications of this type. This is because the expression“transparent glazing” mentioned above covers any type of glazingconsisting of at least one glass sheet and/or of at least one sheet of aplastic which are intended for applications in the motor-vehicleindustry, the building industry or the domestic electrical applianceindustry.

When products preserved in a refrigerated enclosure have to remainvisible, as is the case in many current commercial premises, therefrigerated enclosure is equipped with glazed parts which convert itinto a refrigerated “display case”, the usual name for which is“refrigerated sales cabinet”. There are several alternative forms ofthese “display cases”. Some of them are in the form of a cabinet andthen it is the door itself which is transparent, while others are in theform of chests and it is the horizontal lid which is glazed in order toallow the contents to be seen.

In these types of display cases, it is necessary for the merchandise toremain perfectly visible to customers so that it is possible topreselect the merchandise without opening the “display case”.

When the usual insulating glazing is used, the insulation is not perfectand the temperature of the surface of the glass sheet in contact withthe ambient atmosphere is often below the temperature of the dew point,which may result in the phenomenon of condensation on this surface,affecting visibility.

The use of vacuum insulating glazing makes it possible to eliminate thisdrawback by providing very greatly enhanced insulation. Such insulationalso has the advantage of reducing the energy costs.

The French patent application filed in the name of Saint-Gobain Vitrageunder the number FR 97/09772 describes such a door of a refrigeratedenclosure which includes a vacuum glazing unit. It thus proposes a doorof a refrigerated enclosure essentially consisting of an insulatingpanel composed of at least two glass substrates between which a vacuumhas been created, which substrates are separated from each other bystuds distributed over the entire surface and are joined around theirperiphery by an inorganic seal. In this way, the conventional insulatingglazing units normally used are replaced with one insulating glazingunit consisting of at least two glass sheets between which a vacuum hasbeen created, which we will call hereafter vacuum insulating glazing.This type of vacuum insulating glazing has, for a total thicknessmarkedly less than that of the conventional insulating glazing units,substantially improved thermal insulation properties.

Furthermore, the structure of such a vacuum insulating glazing unit hasthe advantage of giving it a stiffness and a strength which areequivalent to those of a single glazing unit of thickness equal to thesum of the thicknesses of the glass sheets, that is to say the glasssheets behave as a single sheet whose thickness is the sum of that ofthe two glass sheets. In this way, it is not necessary to combine thistype of glazing with a support frame. Thus, the overall size is greatlyreduced and it is very simple to fit it into the environmentalenclosure.

Such a door of a refrigerated enclosure, essentially consisting of avacuum insulating glazing unit, makes it possible to solve the problemof condensation on the external surface: this is because the thermalinsulation of this glazing unit makes it possible to obtain an externalsurface at the ambient temperature.

On the other hand, this enhanced insulation means that the internalsurface of the glazing or of the door is at the temperature of therefrigerated environment, something which accentuates the condensationphenomenon when the door is opened: the temperature of the internalsurface is such that, in the case of freezer cabinets, frosting may beseen to form on the said surface.

The usual techniques for preventing the condensation and/or frostingwhich forms on the internal surface of the doors consist in blowingheated air over this surface. Whatever the technique used, the energycost is high; the cost penalty is even greater in the case of a vacuuminsulating glazing unit, the time required to remove the condensationand/or the frosting being longer. Moreover, this longer time due to thevery low temperature of the internal face goes counter to the intendedaim which consists in obtaining an almost permanent area of visibility,including after opening the door.

The objective of the invention is thus in particular to produce a doorof a refrigerated enclosure which includes a glazed area consisting ofan insulating glazing unit, in which the frosting liable to form on theviewing area when the door is opened can be rapidly and inexpensivelyremoved.

This objective is achieved according to the invention by a transparentglazing unit having at least one viewing area, this area being combinedwith an antifrosting absorbent layer deposited on at least one surfaceof the said area.

The antifrosting function of the layer means that it inhibits theformation of water crystals.

Such a glazing unit, especially when it is an insulating glazing unitand more particularly a vacuum insulating glazing unit, can be used in adoor of a refrigerated enclosure having at least one viewing areaconsisting, for example, of the said vacuum insulating glazing unitcombined with an absorbent layer advantageously deposited on thatsurface of the said viewing area which is in contact with therefrigerated environment.

It has been shown that such a door, comprising the glazing according tothe invention, makes it possible to prevent the frosting phenomenon, ormore precisely to delay it or at the very least limit its appearance.

According to a first embodiment, the antifrosting absorbent layer isdeposited directly on the glass, and more specifically on that surfaceof the vacuum insulating glazing unit which is in contact with therefrigerated environment. This is the surface in contact with therefrigerated environment when the door is in its closed position. Such alayer may be deposited by techniques of the sputtering or coating type,especially of the flow-coating or deep-coating type, the depositionbeing carried out before or after manufacturing of the vacuum glazingunit. Advantageously, an adhesion primer of the silane type is provided;it is either deposited beforehand on the glass or at the same time asthe layer is formed, the silanes being introduced into the compositionof the antifrosting absorbent layer.

According to a second embodiment, the antifrosting absorbent layer isdeposited, for example according to one of the abovementioned methods,on a plastic film and the plastic film is itself fastened to the vacuuminsulating glazing unit. The plastic film used is advantageously apolycarbonate film preferably having a thickness of less than 3millimetres; this plastic is especially chosen for its mechanicalstrength properties. The plastic film is fastened to the glazing in asealed manner so that no trace of moisture can exist between the glasssurface and the plastic film. It may be fastened, for example, byadhesive bonding around the periphery; the air layer possibly existingbetween the glass and the plastic film must then advantageously notexceed 3 mm. The fastening may also be achieved by means of an aluminiumframe combined with a desiccant and an adhesive, similar to that for aninsulating glazing unit of conventional construction; advantageously,the air layer between the glass and the plastic film then does notexceed 10 mm.

According to an advantageous embodiment of the invention, theantifrosting absorbent layer consists of at least one hydrophilicpolymer. Such a polymer may be non-limitingly chosen from the followingpolymers: a polyvinylpyrrolidone of the poly(N-vinyl-2-pyrrolidone) orpoly(1-vinylpyrrolidone) type, a polyvinylpyridine of thepoly(N-vinyl-2-pyridine) type, of the poly(N-vinyl-3-pyridine) type orof the poly(N-vinyl-4-pyridine) type, a polyacrylate of thepoly(2-hydroxyethyl acrylate) type, a polyacrylamide of thepoly(N′,N-hydroxyacrylamide) type, a polyvinyl acetate, apolyacrylonitrile, a polyvinyl alcohol, a polyacrolein, a polyethyleneglycol or a polyoxyethylene. It may also be a copolymer based on two ormore of the abovementioned polymers.

Preferably, the invention specifies that the layer consists of at leastone crosslinked hydrophilic polymer. Crosslinking the polymer makes itpossible, in particular, to obtain better cohesion of the layer and thusto prevent any risk of the layer being dissolved by water, over the longor short term.

According to a preferred embodiment of the invention, the hydrophilicpolymer is combined with an organic or inorganic absorbent material, thesaid absorbent material preferably being porous.

An inorganic absorbent material especially improves the mechanicalstrength of the layer and more particularly prevents the formation ofscratches. The inorganic function is advantageously achieved bydepositing a mesoporous material (CPG-MCM 41), such as TiO₂nanoparticles, or by depositing orthosilicate hydrolysis condensationproducts, or other silicon derivatives.

An organic absorbent material especially allows retention of thehydrophilic polymer; a polyurethane is used, for example.

The inventors have thus been able to demonstrate that the presence of aporous layer which includes a hydrophilic polymer on the surface of theglazed area allows water to be absorbed. This principle prevents theformation of water droplets and thus the formation of a film liable tofrost over and affect visibility through the glazed area. The choice ofhydrophilic polymer and of the porosity in the case of a porousabsorbent material make it possible to control the antifrostingbehaviour of the layer. In particular, increasing the porosity allowsthe rate of water absorption and the water absorptivity, as well as thelevel of water in microdroplet form, to be controlled.

According to a preferred embodiment of the invention, the porosity ofthe layer is between 0.1 and 1000 cm³/g. In the case of a polymericmaterial, it is advantageously between 0.1 and 100 cm³/g and preferablyless than 20 cm^(3/)g. It is preferably between 200 and 1000 cm^(3/)g inthe case of a mesoporous material. The porosity defines the void volumeof the pores per unit mass of the layer.

Also preferably, the layer has pores whose mean diameter is between 0.05and 50 microns, preferably between 0.1 and 20 microns and morepreferably between 1 and 15 microns. The shapes of the cavities makingup the pores are oval or spherical.

Whatever the nature of the antifrosting absorbent layer and the methodof producing the latter, it advantageously has a thickness of less than100 microns, preferably less than 50 microns and more preferably lessthan 35 microns and, in some cases, preferably less than 25 microns andmore preferably less than 20 microns.

Further details and advantageous characteristics of the invention willemerge below from the description of illustrative examples of theinvention and of tests carried out.

As described above, a door or a refrigerated sales cabinet was produced.It consists especially of a vacuum insulating glazing unit in order toform the viewing area and of a door frame, for example made of metal.This frame may especially support all the mechanical systems of thehandle and hinge type, as well as the seals which seal against the wallsof the refrigerated enclosure.

The insulating glazing unit consists of two glass sheets between which avacuum has been created. The glass sheets are separated from each otherby studs distributed over the entire surface of the glazing and arejoined together around their periphery by a seal of inorganic adhesive.Such a vacuum insulation glazing unit is, for example, producedaccording to a technique as described in Patent Application EP 645 516.

According to the invention, a polycarbonate film having a thickness of 2millimetres is fastened to the vacuum insulating glazing unit by meansof an adhesive forming a strip with a thickness of 1 millimetre aroundthe periphery of the glazing. Thus, an air cavity is formed between theglazing and the completely sealed polycarbonate film. This complex isproduced in such a way that the trapped air is dry. The film is fastenedto that side of the vacuum insulating glazing unit which is intended toface the inside of the refrigerated enclosure when the door is in itsclosed position.

Before attaching it, the polycarbonate film is coated with anantifrosting absorbent layer, this being deposited so as to face theinside of the refrigerated enclosure when the door is in the closedposition. The layer thus deposited forms a polymeric porousthree-dimensional network based on polyvinylpyrrolidone andpolyurethane.

Measurements were carried out on the layer in the wet state usingtransmission electromicroscopy; these measurements allow the thicknessof the layer and the size of the pores to be checked. The thickness ofthe layer is equal to 14.5 microns and the pores have a mean diametervarying from 1 to 8 microns.

Tests were carried out on. various types of doors. These doors arefitted onto refrigerated sales cabinets within which a temperature of−28° C. is maintained. The cabinets themselves are placed in anatmosphere at a temperature of 25° C. The tests consist in opening thedoor for a period of 3 minutes and a period of 12 seconds. The 3-minuteperiod simulates the average time needed for this type of cabinet to bestocked up in the morning. The 12-second duration simulates the averagetime needed for a consumer to take one or more products.

The measured results are the times needed for satisfactory visibilitythrough the door to return, that is to say the times needed to removethe condensation and/or frosting.

The first door tested, A, has an insulating glazing unit consisting ofthree glass sheets. The second door tested, B, has a vacuum insulatingglazing unit.

The third door, C, is that according to the invention that has just beendescribed.

The results are given in the table below: 3-min opening 12-s opening A 8 min 20 s 1 min 15 s B 31 min 10 s 1 min 40 s C 0 s 0 s

From these results it is clearly apparent that door C, producedaccording to the invention, prevents the formation of frosting.

Another test was carried out under similar conditions. Only the natureof the layer differs in this second example. This second exampleconsisted in depositing a layer consisting only of a hydrophilicpolymer; this hydrophilic polymer was based on polyvinylpyrrolidone,having a molecular mass of 1,300,000 g/mol and diluted to 10% by mass inethanol. The composition thus obtained was then deposited on the glassby flow coating.

Tests such as those described above, consisting in opening the door fora period of 12 seconds and for 3 minutes, were carried out. In bothcases, there was no sign of any frosting on the viewing area of thedoor.

The presence of the absorbent layer therefore prevents the formation offrosting when the door is opened under normal operating conditions.

1-14. (canceled).
 15. A transparent glazing comprising at least oneviewing area, wherein the viewing area is combined with an antifrostingadsorbent layer deposited on at least one surface of said area.
 16. Theglazing according to claim 15, wherein the layer is deposited on thesurface of the glazing.
 17. The glazing according to claim 15, whereinthe layer is deposited on a plastic film and said plastic film isfastened to the glazing.
 18. The glazing according to claim 15, whereinthe layer comprises at least one hydrophilic polymer.
 19. The glazingaccording to claim 18, wherein the hydrophilic polymer is crosslinked.20. The glazing according to claim 18, wherein the hydrophilic polymeris a polymer or copolymer of vinylpyrrolidone.
 21. The glazing accordingto claim 18, wherein the layer further comprises an organic or inorganicabsorbent material.
 22. The glazing according to claim 15, wherein thelayer in the wet state has a porosity of between 0.1 and 1000 cm³/g. 23.The glazing according to claim 15, wherein the layer in the wet statehas pores whose diameter is between 0.05 and 50 microns.
 24. The glazingaccording to claim 15, wherein the antifrosting adsorbent layer has athickness of less than 100 microns.
 25. The glazing according to claim15, wherein the glazing is an insulating glazing unit comprising atleast two glass sheets.
 26. The glazing according to claim 25, whereinthe glazing is a vacuum insulating glazing unit.
 27. The glazingaccording to claim 21, comprising an inorganic absorbent material,wherein the inorganic absorbent material is porous.
 28. The glazingaccording to claim 15, wherein the layer in the wet state has poreswhose diameter is between 0.1 and 20 microns.
 29. The glazing accordingto claim 15, wherein the layer in the wet state has pores whose diameteris between 1 and 15 microns.
 30. A refrigerated door enclosurecomprising the glazing according to claim
 15. 31. The glazing accordingto claim 18, wherein the antifrosting adsorbent layer is deposited onthe surface of the viewing area which is in contact with a refrigeratedenvironment.